Many metals used in constructions in contact with hydrogen are sensitive to hydrogen, e.g. such used in electrochemical cells for production of alkali metal chlorate. Various solutions have been proposed to overcome this problem.
U.S. Pat. No. 3,992,279 discloses an electrode assembly comprising a Ti-based anode, a cathode, of an iron-based material, and an intermediate layer, of silver or gold, in between said anode and cathode. In an electrolytic cell, e.g. for production of sodium chlorate from sodium chloride, a portion of adsorbed atomic hydrogen deriving from the cathodic reaction at the cathode will start to diffuse from the cathode through the electrode assembly towards the hydrogen-sensitive anode, i.e. the titanium layer. The intermediate layer of the electrode provides for a hydrogen barrier which blocks the flow of hydrogen thereby providing protection of the hydrogen sensitive anode. CA 914,610 also discloses an electrolytic cell assembly, of a multi-monopolar cell, comprising a cathode-intermediate layer-anode structure.
However, in U.S. Pat. No. 3,992,279, atomic hydrogen will recombine to hydrogen gas at the interface zone, i.e. the joint between the cathode and the intermediate layer. This may lead to formation of hydrogen blisters which, in turn, will reduce the strength of the cathode-intermediate layer joint of the electrode assembly as a consequence of the increased pressure which may cause separation thereof.
U.S. Pat. No. 4,116,807 shows one concept of how the formation of hydrogen blisters can be prevented. It discloses a method for connecting, by use of explosion bonding, anode and cathode backplates, carrying an anode and a cathode, to metallic strip conductors, thereby forming an air space between the backplates, which in turn allows hydrogen gas to escape. Explosion bonding, or explosive welding, as such, has been known for a long time to join and reinforce metal constructions. This is described in e.g. an article by Gonzalez, A. et al. pages 199-207 “Explosive welding of Aluminium and Aluminium Alloy Sheet Composites”, 7th International Conference on High energy rate fabrication, Sep. 14-18, 1981, in which aluminium constructions are reinforced with steel meshes. Explosive bonding technique is also described in U.S. Pat. No. 3,137,937.
In assemblies as described in U.S. Pat. No. 4,116,807, however, the explosion bonded backplates are difficult and complicated to manufacture due to the difficulties to distribute energy evenly on the surface on which the strips are placed. The strips can therefore also be difficult to explosion bond at specific fixed points on the backplates. Another drawback with this type of embodiments is that the connection area, which is unventilated, between the strips and the backplates must be considerably large to guarantee good strength and good electrical contact. Further, these types of electrode constructions are only applicable to multimonopolar cells and cell lines, i.e. cells in which the backplates are placed between the cells.